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Keywords:

  • anaemia;
  • cancer;
  • erythropoietin;
  • erythropoietin receptor;
  • survival

Summary

  1. Top of page
  2. Summary
  3. Conclusions
  4. Acknowledgement
  5. References

Randomized clinical studies, carried out in patients with haematological malignancies and with solid tumours, have consistently demonstrated that treatment with recombinant human erythropoietin (Epo) increases haemoglobin levels, reduces blood transfusion requirements, and improves the quality of life. In addition, identification of erythropoietin receptor (EpoR) expression on many types of non-erythroid and cancer cells has spurred an interest in the extra-haematological activities of Epo itself and other erythropoiesis-stimulating agents (ESAs). Epo and its derivatives have emerged as major tissue-protective cytokines in ischaemic and degenerative damage of cardiovascular, neurological and renal diseases, while their angiogenetic and immunomodulatory properties indicate that their therapeutic potential may extend well beyond erythropoiesis alone. Both preclinical and clinical data, however, have suggested that they may contribute to tumour progression and prejudice survival when administered to anaemic cancer patients, though the results are equivocal and the assumed mechanisms by which tumour growth could be promoted are not fully understood. While these findings offer new perspectives, they nonetheless demand caution in the employment of ESAs. Further, well-designed experimental and clinical studies are warranted.

Recombinant human erythropoietin (rHuEpo), also called epoetin, entered clinical practice in the late 1980s for the treatment of anaemia associated with renal failure and was later employed for the management of chemotherapy- or radiotherapy-induced anaemia in cancer patients. Randomized clinical studies have consistently shown that it increases haemoglobin (Hb) levels, reduces red blood cell (RBC) transfusion requirements, and improves the quality of life (Spivak, 1994; Dammacco et al, 1998, 2001; Littlewood et al, 2001; Boogaerts et al, 2003; Hedenus et al, 2003; Osterborg et al, 2005; Witzig et al, 2005).

Three erythropoiesis-stimulating agents (ESAs) are currently used in clinical practice, namely epoetin alfa (Procrit®; Ortho Biotech, Bridgewater, NJ, USA; Epogen®; Amgen, Thousand Oaks, CA, USA; Eprex®; Janssen-Cilag, Cologno Monzese, Milan, Italy), epoetin beta (NeoRecormon®; F. Hoffmann-La Roche, Basel, Switzerland) and darbepoetin alfa (Aranesp®; Amgen), which is a hyperglycosylated Epo analogue with an extended serum half-life compared to rHuEpo. These agents are administered subcutaneously and have comparable profiles of effectiveness and safety. More recently, a third-generation molecule, namely continuous erythropoietin receptor activator (CERA: Mircera®; Roche), with a longer half-life than either epoetin or darbepoetin alfa, has been proposed for the management of chronic kidney disease and is currently under experimental and clinical investigation (Macdougall, 2005). Several studies, motivated by the growing evidence of erythropoietin receptor (EpoR) expression on non-erythroid cells (Arcasoy, 2008) and on various types of malignant tumour cells (Hardee et al, 2006), have also shown that ESAs are endowed with biological and tissue-protective effects. At the same time, however, the possibility that they may modulate cancer cell growth, favour tumour progression, and reduce overall survival has equally been put forward as a cause for concern.

There is thus an obvious need to redefine the role and use of ESAs through revision of current guidelines in clinical practice in order to achieve the maximum benefit, and reduce the risks that may be associated with their administration. In March 2008 members of the Oncology Drug Advisory Committee (ODAC) of the U.S. Food and Drug Administration convened to discuss and disseminate the cumulative data on the safety of ESAs in cancer patients, to indicate further restrictions and to recommend additional double-blind, placebo-controlled studies with primary endpoints of overall survival. Similar actions have been pursued by other regulatory agencies worldwide. The UK Medicines and Healthcare products Regulatory Agency (MHRA), for example, has included rHuEpo in the list of drugs under intensive surveillance.

This article reviews the biological effects of ESAs, their efficacy and tolerability, and the results of preclinical and clinical investigations of their influence on tumour cell growth and the survival of anaemic cancer patients. Current views with regard to the expression of EpoR in non-erythroid cells and the non-haematopoietic functions related to the Epo-EpoR signalling are also discussed.

ESAs and haematological functions

Erythropoietin (Epo) is a 30·4 kDa glycoprotein hormone that regulates erythropoiesis and is normally secreted by the adult kidney and the fetal liver. Its gene expression is mainly affected by decreased tissue oxygen tension via activation of the transcription factor HIF-1 (hypoxia inducible factor-1), which binds a site in the 3′ enhancer of the gene, and increased mRNA stability (Ebert & Bunn, 1999; Fandrey, 2004). Physiologically, Epo prevents apoptosis and stimulates the proliferation and terminal differentiation of cells committed to the erythroid lineage by binding to a specific receptor (EpoR) expressed on their surface. EpoR is a 55 kDa protein that is modified by glycosylation and phosphorylation to 72–78 kDa. It is a dimeric receptor and belongs to the cytokine receptor family; its structure is characterized by conserved motifs in the extracellular domain (four conserved cysteines, a group of aromatic residues and a WSXWS motif), a transmembrane preformed dimer that changes conformation upon binding of its ligand, and an intracellular domain required for signalling cascades (Fig 1).

image

Figure 1.  Signal transduction pathways activated when Epo binds to Epo receptor. EPO, erythropoietin; EPOR, erythropoietin receptor; JAK2, Janus kinase-2; STAT5, signal transducer and activator of transcription-5; PLC-γ, phospholipase C-γ; PI-3K, phosphatidylinositol 3-kinase; NF-kB, nuclear factor κ-B; FKHRL1, member of forkhead family transcription factor; SHIP-1, SH2-containing inositol phosphatase-1; SHIP-2, SH2-containing inositol phosphatase-2; Grb2, growth factor receptor-bound protein-2; CIS, cytokine-inducible SH2-protein; GAB-2, growth factor receptor-bound protein associated binder-2; GAP, GTPase activating protein; SOS, son of sevenless; MEK, mitogen-activated protein kinase/ERK kinase; IRS-2, insulin receptor substrate-2; ERK1/2, extracellular signal-regulated kinase1/2; Shc, Src homologue and collagen adaptor protein; IkB, Inhibitor of NFkB; P, phosphorylated protein. The dotted arrows indicate proposed alternative pathways leading to activation of NF-κB in non-erythroid cells.

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Epo/EpoR-induced signals result in the autophosphorylation of Janus kinase JAK2, a member of the family of tyrosine kinases. It is constitutively associated with EpoR homodimers and mediates the rapid phosphorylation of eight conserved tyrosine residues (PY) of cytoplasmic EpoR that act as fastening sites for various signal transduction proteins (Tilbrook & Klinken, 1999). One of these, transcription factor STAT-5 (signal transducer and activator of transcription-5), is recruited to the receptor complex. Following activation via PY 343, it dimerises and moves to the nucleus where it promotes the transcription of target genes, such as OSM and PIM1, that enhance erythroblast survival, the signalling inhibitor CIS/cytokine-inducible SH2-protein and SOCS (members of suppressor of cytokine signalling family), and Bcl-x (an anti-apoptotic protein). Some of these PY sites are negative regulatory domains of EpoR insofar as they recruit molecules that inactivate signalling, such as tyrosine phosphatase SHIP-1, which dephosphorylates PY 429 and JAK-2 (Klingmuller et al, 1995), or CIS3/SOCS-3 which binds PY 401 (Sasaki et al, 2000) and another EpoR tyrosine motif with PY 429 and PY 431, and interferes with the activation of JAK2/STAT-5 (Hortner et al, 2002).

Other SH2-containing proteins, namely PI3K (phosphatidylinositol 3-kinase), Grb2/Shc and PLCγ (phospholipase C-γ), are activated in the Epo response (Bouscary et al, 2003). In addition, activation of the Ras/MAP kinase pathway is associated with EpoR and plays an important role in Epo-dependent cell proliferation and the regulation of gene expression (Klingmuller, 1997). Lastly, an experimental study has demonstrated Epo-mediated activation of the transcription factor nuclear factor (NF)-κB signalling pathway without involvement of JAK2 (Bittorf et al, 2001).

Menon et al (2006) have shown that the PY343-STAT-5 pathway has a selective and crucial role in the regulation of erythropoiesis during both acute haemolytic anaemia and anaemia associated with chemotherapy and bone marrow transplantation. This emphasizes the difference in level of EpoR signalling between steady-state and stress-induced erythropoiesis, and demonstrates that in STAT-5a,b−/− mice this pathway promotes oncostatin-M, but not Bcl-x expression, both of which enhance the survival of erythroid progenitors.

ESAs and extra-haematological functions

Many non-erythroid cell types are known to express EpoR: vascular endothelial cells, astrocytes and neurons, myoblasts, smooth muscle cells, cardiac myocytes, and retina, kidney and mammary epithelial cells (Arcasoy, 2008). Its specific function in most of these cell types is still poorly understood, though some tissue-protective biological functions associated with its activation in non-haematopoietic cells by exogenous or endogenous Epo have been observed. In vitro and animal studies have shown that these functions are mediated by a surface receptor that is structurally different from the receptor that controls erythropoiesis and characterized by interaction with βcR subunit of the interleukin-3 receptor (Brines et al, 2004). The precise role of this interaction has not been elucidated. Even so, these results support the view that the Epo-EpoR signalling activation mechanisms associated with erythropoiesis and tissue-protective functions of Epo are not the same. Although the βcR subunit was initially claimed to be involved in erythroid progenitor signalling (Shikama et al, 1996), a recent study on differentiated neuroblastoma SH-SY5Y and pheochromocytoma PC-12 cells indicated that, in these types of cells, the cytoprotective anti-apoptotic effect is mediated by the normal homodimer EpoR in a manner similar to haematopoietic cells (Um et al, 2007).

The effects of Epo on vascular endothelial cells and in the regulation of physiological and pathological angiogenesis have been extensively demonstrated. In vitro, the Epo-EpoR system promotes the proliferation, migration and differentiation of normal endothelial cells into vascular tubes and hence the formation of new blood vessels (Carlini et al, 1995; Haller et al, 1996), whereas in vivo it stimulates chick embryo development (Ribatti et al, 1999), wound healing (Haroon et al, 2003), and oestrogen-dependent cyclical angiogenesis in the uterus (Yasuda et al, 1998). Its involvement in the pathological angiogenesis of proliferative diabetic retinopathy (Watanabe et al, 2005) and tumours (Hardee et al, 2006) has also been demonstrated, even though its role in cancer progression is by no means certain.

It is noteworthy that tissue neovascularization has emerged as a source of Epo’s cardioprotective effects in animal models of myocardial infarction, probably through its mobilization of endothelial progenitor cells from bone marrow into the blood (Heeschen et al, 2003; van der Meer et al, 2005; Silverberg et al, 2005). Administration of Epo before or up to 12 h after coronary artery ligation reduced cardiac myocyte apoptosis and overall impairment of cardiac function (Calvillo et al, 2003; Moon et al, 2005). A pilot study has since been conducted to examine the effect of darbepoetin alfa in non-anaemic patients with acute myocardial infarction. A single i.v. 300 μg dose was both safe and well tolerated, whereas the left ventricular ejection fraction at 4 months was similar to that of patients who did not receive additional medication before primary coronary surgery. Further clinical trials are evidently required to establish the efficacy of Epo in patients with cardiac ischaemia (Lipsic et al, 2006). Epo is also protective against cardiotoxicity due to chemotherapeutic agents, such as doxorubicin (Hamed et al, 2006). These results indicate that Epo-mediated cardioprotection is mainly dependent on the signalling PI3K-AKT pathway (Tramontano et al, 2003), though the phosphorylation of other proteins, such as MAP kinases ERK-1/2, has been demonstrated (Fu & Arcasoy, 2007).

The biological and tissue-protective effects of Epo have also been widely investigated in the nervous system and kidney. It has indeed been shown in vitro that rHuEpo protects embryonal, hippocampal and cortical neuronal cells presenting EpoR from cell death induced by neurotoxic molecules and hypoxia (Liu et al, 2006; Won et al, 2007). This effect has been associated with increased hypoxia-induced EpoR expression and sensitivity to Epo (Yu et al, 2002).

More recent in vivo studies have reported that Epo produced in the mouse central nervous system during chronic hypoxia protects the brain. This protection, in fact, is abolished by infusion of a soluble form of EpoR and neuronal degeneration ensues (Sakanaka et al, 1998). Other studies of rats as experimental models of stroke have indicated that systemic administration of rHuEpo before or up to 6 h after ischaemic brain injury reduces the extent of cerebral infarction after crossing the blood-brain barrier (Brines & Cerami, 2005), as well as in humans, whose functional outcome is improved when it is administered within 8 h after stroke (Ehrenreich et al, 2002).

The neuroprotective effect of Epo in the peripheral nervous system takes the form of reduction of the axonal degeneration typical of peripheral neuropathies (Toth et al, 2008), while experimental studies have confirmed its positive role in the prevention and treatment of both diabetic neuropathy and polyneuropathy induced by chemotherapeutic agents, such as cisplatin and paclitaxel (Bianchi et al, 2004, 2006; Melli et al, 2006).

As in the case of haematopoietic cells, in neuroprotection, many signalling pathways, including JAK-2/STAT-5, ERK-1/-2 and PI3K/AKT, are simultaneously activated after endogenous Epo stimulation in the ischaemic brain, particularly in mediating the anti-apoptotic effect (Kilic et al, 2005). However, the intracellular signalling pathway seems to involve JAK2 and the nuclear transcription factor NF-κB, which triggers NF-κB-dependent transcription of neuroprotective genes and, probably, inhibitory proteins of apoptosis (Digicaylioglu & Lipton, 2001).

Protection of the kidney by Epo has not been definitely established. In vitro studies have shown its direct effect on proliferation and cell death in proximal tubular epithelial cells, while in experimental models of acute renal failure it reduces tubular cell death and hence the dysfunction induced by ischaemia reperfusion injury (Sharples & Yaqoob, 2006). Benefits of Epo have been reported in animal models of systemic shock and nephrotoxicity induced by cisplatin and ciclosporin (Bagnis et al, 2001; Lee et al, 2005). In contrast, in a model of radiation-induced kidney dysfunction, protective administration of Epo was disappointing because it was associated with deterioration of renal function (Andratschke et al, 2006).

In the last few years, the effect of Epo on immunity has emerged in reports of tumour regression in murine myeloma models as the result of a T CD8+ cell-mediated immune response (Mittelman et al, 2001). Other studies by the same authors have indicated that Epo may be associated with prolonged survival in patients with advanced multiple myeloma (Mittelman et al, 2004). It is suggested that this anti-myeloma effect could be related to immune system modulation, given that Epo induces normalization of CD4/CD8 cell ratio, enhances T-cell phytohaemagglutinin-mediated activation and potential proliferation, reduces the percentage of CD8+ T cells expressing the inhibitory molecule CTLA-4 (cytotoxic T lymphocyte-associated 4) and increases CD8+ T cells expressing the costimulatory CD28 (Prutchi-Sagiv et al, 2006). Some of these results have also been confirmed by other workers (Baz et al, 2007).

Epo and EpoR in tumours: the preclinical experience

Many experimental studies have shown Epo-R expression in a variety of tumour cell lines. EPO mRNA transcripts and proteins, also induced by hypoxia, were detected in the cytoplasm of hepatocarcinoma cells, melanoma, breast, colon, pancreas, gastric, ovarian, uterine, renal, bladder, prostate, non-small-cell lung, head and neck carcinoma, and B-cell haematological malignancies (Hardee et al, 2006; Kokhaei et al, 2007). However, there is at present a considerable controversy on the techniques used for EpoR detection, such as Western blot, immunoprecipitation and immunohistochemical analysis, that are unable to distinguish EpoR expression on cell surface (where it is normally activated by Epo) from intracellular location. In addition, expression (or RNA) of a protein does not necessarily mean that it is functional. This point has been clearly addressed in the pivotal editorial of Longmore (2007). Moreover, most studies have identified EpoR by using non-specific commercially available anti-EpoR antibodies, which can also bind multiple proteins with different molecular size (Elliott et al, 2006). Similarly, sensitive reverse-transcription polymerase chain reaction (RT-PCR) analysis has been shown to identify EPOR mRNA transcript, but this evidence does not necessarily mean its translation into functional EpoR expression. Recently, two reports have evaluated EpoR cell surface expression in tumour cells through EpoR binding studies with radiolabeled Epo (LaMontagne et al, 2006; Um et al, 2007); the first report emphasized the absence of measurable Epo-specific binding activity and the second, a very low number (fewer than 50 molecules/cell) of high affinity surface binding sites compared to erythroid cells. Taken together, these findings suggested that EpoR protein can be synthesized but not carried to the cell surface, probably because of the lack of accessory trafficking factors (Sinclair et al, 2008).

Another essential issue is whether EpoR is able to elicit a biological response of tumour cells to binding with Epo, through the transduction of EpoR-mediated signalling pathways. Numerous in vitro studies have shown Epo-induced activation of the major EpoR signalling cascades in various cancer cell lines (Lai et al, 2005; Lester et al, 2005; Mohyeldin et al, 2005; Kumar et al, 2006; Um & Lodish, 2006; Hamadmad & Hohl, 2008; Jeong et al, 2008), associated with increased tumour cell migration, invasion and apoptosis inhibition, while upregulation of Epo and EpoR expression during hypoxia suggested the establishment of a supportive autocrine loop (Lester et al, 2005; Mohyeldin et al, 2005). Nevertheless, most studies failed to show tumour cell proliferation following stimulation by Epo and only a few papers have reported a limited increase in vitro in the proliferation of breast, renal and prostate carcinoma cells (Westenfelder & Baranowski, 2000; Acs et al, 2001; Feldman et al, 2006), generally using supra-physiological doses of Epo. However, Dunlop et al (2006, 2007) reported the activation of Epo/EpoR signalling in non-small-cell lung carcinoma at pharmacological concentrations of Epo, even if it was not associated with a growth promoting effect on tumour cells. In addition, it has been more recently shown that expression of a constitutively active EpoR variant in breast cancer cells results in their increased proliferation and migration by activation of the ERK- and SAPK/JNK-dependent pathways, but not JAK-2/STAT-5 axis (Fu et al, 2009), suggesting that EpoR over-expression and activation could favour tumour progression.

Enhanced angiogenesis could also promote tumour growth. rHuEpo stimulates the proliferation and migration of endothelial cells, induces their angiogenic phenotype, increases their metalloproteinase (MMP)-2 secretion, inhibits their apoptosis, and is angiogenic in vivo in the chick embryo chorioallantoic membrane in the same way as fibroblast growth factor-2 (Ribatti et al, 1999). These data point to the existence of an autocrine and paracrine circuit that influences a tumours’ biological behaviour. In addition, blockade of Epo signalling in animal models by antibody to Epo or EpoR antagonists inhibits angiogenesis and survival of tumour cells, and leads to the destruction of tumour masses (Yasuda et al, 2001, 2003). These results have since been confirmed by Hardee et al (2007) in an angiogenic model of fluorescence-labelled mammary carcinoma cells implanted in dorsal skin-fold window chambers in mice. Blockade of the Epo-EpoR system proved to be an effective anti-tumour strategy. This study, however, is in contrast with the previous observation by the same authors of the absence of angiogenic and direct growth promoting effects in rats transplanted with rodent and human tumour cells, and treated with a therapeutic dose of Epo (Hardee et al, 2005).

A closely related question is whether rHuEpo increases sensitivity to radiotherapy or chemotherapy. Experimental studies in rats transplanted with sarcoma or glioblastoma and treated with Epo prior to radiation therapy to prevent anaemia have revealed higher radio sensitivity and delayed tumour growth as compared with anaemic rats, but shorter than non-anaemic animals (Thews et al, 1998; Stuben et al, 2001). In other studies, however, correction of anaemia up to an increased haematocrit has resulted in a lack of radiosensitivity, probably because of enhanced blood viscosity and hence decreased tumour perfusion (Joiner et al, 1993).

The effect of Epo on the response to chemotherapeutic agents has also been investigated, with conflicting results. Inhibition of cisplatin-induced apoptosis was reported by three studies on human cervical cancer, glioblastoma and renal carcinoma cells respectively, treated with rHuEPO at doses from 25 to 200 U/ml (Acs et al, 2003; Belenkov et al, 2004; Li et al, 2007). In contrast, in a study using a lower dose of Epo (10 U/ml) in various cancer cell lines expressing low levels of EpoR, no effect was shown on bcl-2 expression and no modification in responsiveness to subsequent treatment with cisplatin (Liu et al, 2004). However, studies in severe combined immunodeficient (SCID) mice bearing human ovarian cancer cells have provided evidence of a correlation between Epo administration and sensitivity to cisplatin, associated with a 25–35% increase of haematocrit (Silver & Piver, 1999). In other animal models it was demonstrated that correction of anaemia with ESAs during treatment with cyclophosphamide enhances sensitivity to this drug by improving tumour tissue oxygenation and thus delaying cancer growth, compared to the anaemic controls (Thews et al, 2001).

Finally, preclinical studies have clearly shown that there is no worse outcome detectable in animal studies in which tumours have been implanted and ESAs have been used to increase haemoglobin concentrations (reviewed by Osterborg et al, 2007 and Sinclair et al, 2007).

ESAs in the treatment of anaemia in cancer patients

Anaemia is a frequent complication of cancer. It may be its direct consequence or the outcome of chemotherapy treatment, and adversely affects the overall quality of life (Ludwig et al, 2004). It is also a negative prognostic factor because anaemic patients with lung, cervical, prostate, head and neck cancer, multiple myeloma and lymphoma have a shorter survival and a higher relapse rate than non-anaemic patients at the same disease stage (Caro et al, 2001). Correction of anaemia has thus become a primary goal of disease management, especially since the maintenance of adequate Hb levels allows the establishment of an optimal chemotherapy dose and a timely therapeutic programme. Moreover, in patients undergoing radiation therapy for cervical and head and neck cancer, the increase of Hb levels within the normal range may improve intra-tumoural hypoxia, and then enhance radiosensitivity, provide a better local disease control and possibly result in prolonged survival (Dunst, 2001; Shasha, 2001; Harrison et al, 2002). In respect, the advent of epoetin has been of crucial importance in the oncology setting, owing to its improvement of the quality of life, maintenance of the Hb concentration, and reduction of the need for RBC transfusions.

Several placebo-controlled, randomized studies have clearly illustrated these therapeutic benefits in various types of cancer (Vansteenkiste et al, 2002; Chang et al, 2005; Grote et al, 2005; Savonije et al, 2005; Razzouk et al, 2006; Wilkinson et al, 2006; Pirker et al, 2008; Strauss et al, 2008). The most recent studies in patients with solid tumours and haematological malignancies are summarized in Tables I and II. They have consistently demonstrated a significant increase in Hb concentration and a significant improvement of the quality of life compared to the placebo group. The occurrence of side effects, including thromboembolic events, was similar to that of the placebo group, and there were no significant differences in the median overall survival, time to progression and overall mortality.

Table I.   Summary of selected randomized clinical studies on the use of ESAs in patients with haematological malignancies and in mixed haematological/solid tumour populations.
No. of patientsMalignancyTreatmentESADoseHb baseline/Hb stopping value (g/l)ResultsReference
Increased mean Hb (g/l)Transfusion requirementImprovement in QoLMedian survival
  1. Hb, haemoglobin; QoL, quality of life; HR, hazard ratio; CI, confidence interval.

  2. *Percentage of patients obtaining an increase in Hb level of ≥20 g/l without transfusion.

  3. †Evaluation at 9–12 weeks.

145Multiple myelomaChemotherapyEpoetin alfa versus placebo150–300 i/u kg−1 × 3 weekly for 12 weeks<110/14018 vs. 0·0; P = 0·00128% vs. 47%; P = 0·017P ≤ 0·05Dammacco et al (2001)
375Solid or nonmyeloid haematological malignanciesNonplatinum chemotherapyEpoetin alfa versus placebo150–300 i/u kg−1 × 3 weekly for 28 weeks≤105 or >105 ≤120/15022 vs. 5·0; P < 0·00124·7 vs. 39·5%; P = 0·0057P ≤ 0·048At 12 months  60% vs. 49%; P = 0·13Littlewood et al (2001)
344Lymphoproliferative malignanciesChemotherapyDarbepoetin alfa versus placebo2·25–4·5 μg/kg per weekly for 12 weeks≤110/140 (women) 150 (men)26·6 vs. 6·9; P < 0·00131% vs. 48%; P < 0·001P = 0·032Hedenus et al (2003)
262Lymphoid and solid tumoursChemotherapyEpoetin beta versus standard care150–300 i/u kg−1 × 3 per weekly for 12 weeks≤110/14021 vs. 9·0; P < 0·00122% vs. 43%; P < 0·001P < 0·05–0·076Boogaerts et al (2003)
343Lymphoproliferative malignanciesChemotherapyEpoetin beta versus placebo150 i/u kg−1 × 3 weekly for 16 weeks<100/not reported67% vs. 27%*; P < 0·0001P < 0·05 17·4 vs. 18 months (HR 1·04, 95% CI: 0·80–1·36)Osterborg et al (2005)
344All types of cancerChemotherapyEpoetin alfa versus placebo40 000–60 000 i/u weekly for 16 weeks<115 (males) <105 (females)/15028 vs. 9·0; P < 0·000125% vs. 40%; P = 0·005P = 0·1810·4 vs. 11·2 months; P = 0·53Witzig et al (2005)
224Non-myeloid malignanciesChemotherapyEpoetin alfa versus placebo600–900 i/u kg−1 per weekly for 16 weeks <105 (5–12 years) <110 (girls >12 years) <120 (boys >12 years/140–15013 vs. 10; P = 0·00224% vs. 45·2%; P = 0·002†Razzouk et al (2006)
Table II.   Summary of selected randomized clinical studies on the use of ESAs in patients with solid tumours.
No of patientsMalignancyTreatmentESADoseHb baseline/Hb stopping value (g/l)ResultsReference
Increased mean Hb (g/l)Transfusion requirementImprovement in QoLMedian survival
  1. *Percentage of patients obtaining an increase in Hb level of ≥20 g/l or an increase in Hb of 120 g/l without transfusion in the previous 28 d.

  2. †Median duration of progression–free survival.

  3. ‡Percentage of patients obtaining an increase in Hb level of ≥20 g/l.

  4. §Specific duration of treatment not reported.

  5. ¶Percentage of patients with progression of disease.

  6. **Percentage of patients dead at the end of the study.

320Lung cancerPlatinum based chemotherapyDarbepoetin alfa versus placebo2·25–4·5 μg/kg per weekly for 12 weeks≤110/  140 (women)  150 (men)66% vs. 24%*; P < 0·00127% vs. 52%; P < 0·001P = 0·019–0·05222 vs. 20 weeks†; 46 vs. 34 weeks; P not reportedVansteenkiste et al (2002)
316Solid tumoursPlatinum-based chemotherapyEpoetin alfa versus supportive care10 000–20 000i/u × 3 weekly for 4 weeks≤120/14076% vs. 45%*; P < 0·00136% vs. 65%; P < 0·001P ≤ 0·0511 vs. 12 months; P = 0·39Savonije et al (2005)
354Breast cancerChemotherapyEpoetin alfa versus standard care40 000–60 000i/u weekly for 16 weeks≤120/14065·7% vs. 6·3‡; P < 0·00018·6% vs. 22·9%; P < 0·0001P < 0·001Chang et al (2005)
224Small-cell lung cancerChemotherapyEpoetin alfa versus placebo150 u/kg × 3 weekly§≤145/160−2·0 vs. −29; P not reported24% vs. 37%; (HR = 0·597; 95% CI = 0·365–0·977)10·5 vs. 10·4 months; P = 0·264Grote et al (2005)
182Ovarian cancerPlatinum-based chemotherapyEpoetin alfa versus standard treatment10 000–20 000i/u × 3 per weekly for 28 weeks≤120/14016 vs. 3·0; P < 0·0017·9% vs. 30·5%; P < 0·001P = 0·054–0·11811% vs. 2%¶; P = 0·425Wilkinson et al (2006)
 74Cervical cancerRadio-chemotherapyEpoetin beta versus standard care30 000–60 000 i/u per weekly for 12 weeks<120/15013 vs. −7·0; P < 0·000126·5% vs. 30%; P not reported20·6% vs. 3%¶; P = 0·1223·5% vs. 12·5%**; P = 0·22Strauss et al (2008)
600Small-cell lung cancerPlatinum-etoposide chemotherapyDarbepoetin alfa versus placebo300 μg/weekly for 4 weeks; then every 3 weeks§≥90 ≤130/140−11·3 vs. −19·8; P < 0·00140 vs. 40 weeks; P = 0·431Pirker et al (2008)

Some randomized clinical trials, however, have described decreased overall survival and poorer outcome in cancer patients treated with ESAs (Table III). Henke et al (2003) found that, among 351 patients with head and neck cancer undergoing radiotherapy, those who received Epo had a shorter overall survival. The same group later investigated a subset of 154 patients from this trial to determine whether this adverse effect of Epo was restricted to patients expressing the EpoR (Henke et al, 2006). These patients, in effect, displayed a poorer prognosis in terms of loco-regional progression-free survival compared with the placebo group (P < 0·01), while Epo did not affect the outcome in patients with EpoR-negative tumours. Assessment of this work is rendered problematical by the exceedingly high doses administered (60 000 U/week) and the >150 g/l Hb target reached in most patients, since this may have increased blood viscosity and decreased tissue and tumour oxygenation, and hence rendered radiotherapy less effective.

Table III.   Summary of the most important randomized, controlled studies that show decreased survival and/or tumour progression in cancer patients treated with ESAs.
No of patientsMalignancyTreatmentESADoseHaemoglobin baseline (g/l)Haemoglobin target (g/l)ResultsReference
  1. PFS, progression-free survival; OS, overall survival; RR, relative risk.

  2. *The initial worse outcome in EPO-treated patients which caused the interruption of the trial was not confirmed after 2-years’ observation.

351Head and neck cancer (T3, T4 or node positive)RadiotherapyEpoetin beta versus placebo300 i/u kg−1 × 3 weekly for radiotherapy course<120 (women) <130 (men)≥140 (women) ≥150 (men)Reduced locoregional PFS (HR 1·62; P = 0·0008) Reduced time to locoregional progression (HR 1·69; P = 0·007) Reduced OS (HR 1·39; P = 0·02)Henke et al (2003)
939Metastatic breast cancerChemotherapyEpoetin alfa versus placebo40 000–60 000i/u weekly for 12 months≤130 140Reduced 12-months OS (70% vs. 76%; P = 0·01)Leyland-Jones et al (2005)*
 70Non-small cell lung cancer (stage III–IV)Palliative radiotherapyEpoetin alfa versus placebo40 000–60 000i/u weekly for 12 weeks≤120140Reduced OS (HR 1·84; P = 0·04)Wright et al (2007)
522 Head and neck cancer (T2–T4 any N)RadiotherapyDarbepoetin alfa150 μg weekly<140155Increased risk of locoregional failure (RR 1·44; P = 0·03); Reduced OS (RR 1·28; P = 0·08)Overgaard et al (2007)
989Non-myeloid malignanciesNoneDarbepoetin alfa versus placebo6·75 μg/kg every 4 weeks for 16 weeks<120130Reduced OS (HR 1·3 P = 0·022)Smith et al (2008)

An equally important question is the specificity of the antibody used for immunohistochemical staining (C-20 anti-EpoR; Santa Cruz Biotechnology, Santa Cruz, CA, USA). Elliott et al (2006) have shown that this antiserum is not suitable for investigating EpoR expression, as it mostly recognizes HSP70 protein, whose levels are increased in tumours and associated with a worse outcome. However, a more recent study by Brown et al (2007) has reported that the specificity of this antibody assessed by immunohistochemistry can be increased by preincubation of C20 with the synthetic peptide HSP70-2, that abolishes non-specific cytoplasmic staining, but retains membranous staining. Additional criticism concerned the imbalance of risk factors in favour of the placebo group (smoking, tumour relapse before treatment, more advanced stage of disease).

Similar evidence of Epo’s adverse impact on overall survival was provided by a study of 939 metastatic breast cancer patients randomized to receive ESAs or placebo for 12 months (Leyland-Jones et al, 2005). This study was terminated early because of a higher mortality in the ESAs arm in the first 4 months of therapy. However, the randomization design of this study had many limitations because of imbalance of risk factors, such as advanced age, lower performance status, greater extent of disease and a higher risk for thromboembolic events. Further biases were the absence of standard assessment and of important prognostic factors, such as definition of disease site, initial prognosis, specific assessment of tumour response at predefined intervals, and type, duration and dose of chemotherapy (Leyland-Jones, 2003).

A randomized, double-blind, placebo-controlled study involving 70 patients (less than a quarter of the designed 300-patient sample) with advanced non-small-cell lung cancer reported decreased overall survival in those treated with epoetin alfa compared with a placebo (63 vs. 129 d; P = 0·04) (Wright et al, 2007), and was also terminated earlier because of concerns raised in other trials, rather than problems encountered in this study. The recent results of the interim analysis of the Danish Head and Neck Cancer study, which comprised 522 patients with head and neck tumours and had, as the primary end point, loco-regional disease control, demonstrated a poorer outcome in patients randomized to receive darbepoetin alfa (Overgaard et al, 2007). In addition, Smith et al (2008) found a shorter survival of subjects treated with darbepoetin alfa after a 2-year follow-up in a randomized placebo-controlled study of 989 patients with various tumour types not receiving chemotherapy or radiotherapy.

Studies on haematological malignancies have also provided conflicting results. A clinical trial found no difference in survival in 344 patients with multiple myeloma, non-Hodgkin lymphoma, Waldenström macroglobulinaemia, Hodgkin lymphoma and chronic lymphocytic leukaemia, treated with darbepoetin alfa versus placebo (Hedenus et al, 2003, 2005). A retrospective study of 257 patients with multiple myeloma has recently demonstrated that ESAs are associated with improved overall survival in anaemic patients at Southwestern Oncology Group stages II, III and IV [hazard ratio (HR) 0·6; 95% confidence interval (CI) = 0·38–0·94] (Baz et al, 2007). In contrast, another retrospective assessment of 323 myeloma patients treated with ESAs and followed up between 1988 and 2007 has shown their shorter survival (31 vs. 67 months; P < 0·001) and median progression-free survival (14 vs. 30 months; P < 0·001) compared to untreated patients (Katodritou et al, 2008). However, this study has important limitations in its design, especially because of baseline differences between the two groups in the most important prognostic factors for multiple myeloma (higher age, higher International Staging System stage, lower platelet count, haemoglobin levels, serum albumin, higher serum creatinine, lactate dehydrogenase and β2-microglobulin in the ESAs group), as well as in disease stage and lines of treatment (Ludwig et al, 2008).

A meta-analysis by Hedenus et al (2005), of four randomized, double-blind, placebo-controlled studies conducted including lymphoproliferative malignancies and solid tumours and evaluating the impact of darbepoetin alfa on progression-free survival and overall survival did not show differences compared to placebo (HR 0·92; 95% CI = 0·78–1·07; and HR 0·95; CI = 0·78–1·16, respectively).

A recent meta-analysis of 19 randomized controlled studies on 2805 patients with various types of cancer (Bohlius et al, 2005) evaluated the impact of ESAs on overall survival. It showed a trend towards improvement of survival with ESAs (HR 0·84, 95% CI = 0·69–1·02). A subsequent update of this analysis, including additional studies (Bohlius et al, 2006), however, has shown a shift towards decreased survival (HR 1·08, 95% CI = 0·99–1·18; 42 trials and 8167 patients) and an increased risk of thromboembolic events (RR 1·67, 95% CI = 1·35–2·06; 35 trials and 6769 patients). It is suggested that this shift may be related to the inclusion of patients with higher baseline and target Hb levels, and greater doses of ESAs.

Lastly, no effect of epoetin beta on survival and tumour progression was found by Aapro et al (2008) in another meta-analysis of 12 randomized controlled studies comprising 2301 patients with solid tumours and non-myeloid haematological tumours. This study assessed the effects on a subgroup of patients with baseline Hb ≤ 110 g/l, whose analysis demonstrated a significant lower risk of progression.

These data, therefore, provide no convincing evidence of the real impact of ESAs on overall survival in cancer patients, nor whether this impact is related to their correction of anaemia or other biological effects. Although these results require further and appropriately designed clinical trials, they indicate that administration of ESAs in anaemic neoplastic patients demands caution, strict observation of guidelines, and evaluation of both the benefits and the acceptability of risk. Indeed, most clinical trials have used a Hb target concentration >120 g/l, higher than presently recommended, and three studies were conducted outside the currently approved indications (after radiotherapy or in anaemic patients not receiving concurrent chemotherapy).

In view of the reports on the safety of ESAs, the American Society of Hematology and the American Society of Clinical Oncology (ASH/ASCO) updated their clinical practice guidelines in 2007 (Rizzo et al, 2008). They recommend the initiation of ESAs treatment at Hb level ≤100 g/l, an Hb target of 120 g/l, and the payment of close attention to thromboembolic complications, including deep venous thrombosis, pulmonary embolism, angina, myocardial infarction, and stroke. There is abundant evidence that ESAs are associated with thrombotic events (Bohlius et al, 2006). A systematic overview from the Cochrane Collaboration and MEDLINE and EMBASE databases comparing ESAs with placebo or standard care in anaemic cancer patients confirmed a higher thromboembolic risk in patients receiving ESAs (7·5% vs. 4·9%; RR 1·57; 95% CI = 1·31–1·87), and an increased mortality risk (HR 1·10; 95% CI = 1·01–1·2) (Bennett et al, 2008). Previous studies in patients with kidney and heart disease (Besarab et al, 1998) had shown that the increased risk of thromboembolic accidents was related to target Hb levels (140 g/l) and haematocrit value (42%). In this patient setting, in fact, when the Hb concentration ranged between 113 and 135 g/l, no increase of thrombotic risk was reported (Singh et al, 2006). Finally, it should be mentioned that this risk is further increased by a prior history of thromboses, surgery, prolonged immobilization or by treatment with thalidomide or lenalidomide in myeloma patients (Bennett et al, 2006).

Conclusions

  1. Top of page
  2. Summary
  3. Conclusions
  4. Acknowledgement
  5. References

ESAs have been used worldwide for many years on thousands of anaemic patients with cancer, although there is no definite evidence to date that indicates that their use results in increased survival. However, recent studies are both suggesting extension of their administration for the treatment of cerebral ischaemia or myocardial infarction, and expressing concern about their safety. Given that most randomized studies have various limitations in their design, additional randomized, controlled studies should be exploited with the aim of estimating both benefits and harms of ESAs administration in more homogeneous patient subgroups with chemotherapy-associated anaemia.

The role of EpoR, including its exact structure and expression on normal and cancer cells, requires more appropriate investigations. At variance from erythroid progenitor cells, thus far it has not been conclusively shown that ESAs activate EpoR signalling in tumour cells. As excessively high doses of ESAs have been used to detect cell changes, this cannot be considered as conclusive evidence that the EpoR (if expressed on the cell surface at all) is able to provide signalling at concentrations that can hardly be achieved in a tumour in vivo. In addition, their modulated functions are not clear, given that ESAs do not promote cell proliferation and an anti-apoptotic effect. The tumour progression and reduction of overall survival described in some trials may thus be due to other mechanisms. Future preclinical investigations should specifically address the role of ESAs in cancer biology, possibly with the help of animal models. In addition, clinical studies, carefully designed and properly powered, should assess their effects on crucial issues, such as tumour response, quality of life, progression-free and overall survival.

In our opinion, the potential risk asserted for the use of ESAs should be counterbalanced by the observation that long-term treatment (often more than 20 years in anaemic patients with renal failure) has not provided evidence of an increased risk of tumour development or progression.

Acknowledgement

  1. Top of page
  2. Summary
  3. Conclusions
  4. Acknowledgement
  5. References

This work was supported by a grant from Associazione Italiana per la Ricerca sul Cancro (AIRC), Milan, Italy.

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  4. Acknowledgement
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